1. Field of the Invention
The present invention relates to a liquid discharge head configured to discharge liquid such as ink and a recording apparatus including the liquid discharge head.
2. Description of the Related Art
A thermal ink jet system is known as a liquid discharge method of an ink jet recording apparatus configured to discharge ink as liquid to a recording material to perform recording. The thermal ink jet system applies heat to the liquid (ink) to boil the liquid, and uses the foaming power thereof. A recording element substrate is used in a liquid discharge head used in the thermal ink jet system in order to discharge the liquid. The recording element substrate includes a recording element including a plurality of heating resistor elements (heaters) as a liquid discharge unit, a supply flow path configured to supply liquid to the heaters, a supply port configured to supply the liquid to the supply flow path, and a discharge port configured to discharge the liquid according to discharge energy generated in the heaters. In the ink jet recording apparatus, in order to enable higher-speed and higher-quality recording, heaters are densely disposed in the liquid discharge head, and the heaters are driven at high frequency. The power supply required for the liquid discharge head increases with these measures.
When the power supply increases, the temperature rise width of the overall liquid discharge head during driving increases, which may influence discharge performance depending on an achieved temperature. The temperature of the liquid in the liquid discharge head increases. According to this, a liquid discharge quantity also increases. As a result, when the temperature of the liquid discharge head rapidly increases, a recording density increases even if the same image is recorded, which may cause image density unevenness.
For the above reasons, many measures for emitting heat outside have conventionally been taken for the liquid discharge head. A liquid discharge head described in Japanese Patent Application Laid-Open No. 2007-168112 includes a heat transport unit such as a heat pipe in a liquid discharge head to emit heat outside via a heat transport medium such as a coolant. A liquid discharge head described in Japanese Patent Application Laid-Open No. 2004-209764 includes a partial structure formed by using a porous member having holes impregnated with liquid. The liquid impregnating the porous member absorbs the heat of the liquid discharge head, and is ejected outside, to emit the heat outside. This configuration can eject the liquid absorbing the heat in a discharge operation using the liquid to be discharged as impregnation liquid.
However, a further increased recording speed causes a problem. Generally, a recording element substrate is formed into a rectangular shape. The recording element substrate has a long side and a short side of several millimeters to several tens of millimeters and a thickness of several hundreds of micrometers to several millimeters. The recording element substrate includes heaters as a recording element configured to generate energy for discharging liquid. Furthermore, the recording element substrate includes a discharge port group including a plurality of discharge ports formed and arranged in a row so as to correspond to each of the heaters. In recent years, the discharge port group often includes a plurality of rows for the reason described above.
Generally, a liquid discharge head includes a recording element substrate fixed to a supporting member made of a material such as ceramic and a resin by an adhesive agent. A liquid chamber configured to supply liquid to the recording element substrate is formed in the supporting member. The liquid is supplied to the liquid chamber via a liquid chamber inflow port from a liquid tank.
Herein, as described in Japanese Patent Application Laid-Open No. 2004-209764, in the case of the configuration using the porous member, generally, the temperature of the center of the main surface of the recording element substrate is relatively high, and the temperature of the end (outer peripheral portion) of the main surface of the recording element substrate is relatively low. The configuration causes a temperature difference in the in-plane direction of the main surface. The end of the main surface of the recording element substrate is mainly joined to the supporting member by the adhesive agent. For this reason, a quantity of heat transferred to the supporting member is generally larger than that to liquid, causing a larger amount of heat to escape from the recording element substrate to the supporting member side. Thus, the configuration using the porous member cannot solve the problem of deterioration of recording quality caused by the temperature difference in the in-plane direction of the main surface of the recording element substrate, and the issue concerning a cooling unit is left to be solved.
As described in Japanese Patent Application Laid-Open No. 2007-168112, the configuration in which the liquid discharge head includes the heat pipe can improve the temperature distribution of the overall liquid discharge head. However, the configuration makes it difficult to improve the temperature distribution in the in-plane direction of the main surface of the recording element substrate having a region of several tens to several hundreds square millimeter. For this reason, the configuration described in Japanese Patent Application Laid-Open No. 2007-168112 also cannot solve the problem concerning the cooling unit.
Therefore, since the configuration of the conventional liquid discharge head makes it difficult to decrease the temperature difference in the in-plane direction of the main surface of the recording element substrate, it has been difficult to prevent deterioration of recording quality caused by heat in high-speed recording or high-density recording.